1. Field of the Invention
The present invention relates to a non-reducing, dielectric ceramic composition, particularly a dielectric ceramic composition which exhibits a high dielectric constant, a small change in the dielectric constant depending upon temperature, a small secular change, a stable dielectric constant when DC bias is applied, a low dielectric loss, and a high resistivity, and which can be fired at a relatively low temperature.
The present invention also relates to a monolithic capacitor.
2. Description of the Related Arts
Barium titanate provides a dielectric ceramic composition exhibiting a high dielectric constant, a small change in the dielectric constant and a small dielectric loss, when it is doped with cobalt-, tantalum-, or samarium-niobate, bismuth stannate, or bismuth-, tantalum-, or niobium-zirconate. The thus-provided dielectric ceramic composition makes it possible to produce monolithic ceramic capacitors having a small size and a high capacitance, as disclosed in U.S. Pat. No. 3,920,781. These monolithic ceramic capacitors are used as circuit elements of an IC, broadly for application in communication devices, computers, television-receivers, and the like.
The conventional methods for producing the monolithic ceramic capacitors are as set forth in the preamble of claim 10 and are roughly classified into the printing method and the sheet method. According to the printing method, a slurry of dielectric material is prepared; is printed into a predetermined shape by means of, for example screen printing, followed by drying; an electrode paste is printed on the dried dielectric material; and a next layer of the dielectric material is printed. This procedure is repeated to form a monolithic. According to the sheet method, a sheet of dielectric material is produced by, for example, the doctor blade method, and an electrode paste is printed on the sheet of dielectric material. This procedure is repeated to produce a plurality of the dielectric material-sheets with an electrode thereon, which are laminated one upon the other and thermally pressure-bonded. The monolithic obtained by this or any other appropriate procedure is fired at a temperature of from 1250.degree. C. to 1400.degree. C. in an ambient atmosphere to obtain a sintered body. External lead electrodes are baked on the sintered body to provide a conduction with electrodes embedded in the interior of a sintered body, i.e., the inner electrodes. Since the inner electrodes are sandwiched between the sheets of dielectric material and both the inner electrodes and the dielectric material are simultaneously fired, the material requirements of the inner electrodes are such that the material be in electrical contact with the dielectric material at its firing temperature, and is neither oxidized at the sintering temperature in the ambient atmosphere nor reacted with the dielectric material at the firing temperature. Noble metals, such as platinum and palladium, meet such requirements and have been used as the electrode material in most cases. Noble metals are very stable but are expensive. Accordingly, the cost of inner electrodes made of a noble metal amounts to approximately 20-50% of the cost of the monolithic ceramic capacitor.
U.S. Pat. No. 3,920,781, Japanese Unexamined Patent Publication Nos. 53-24600 and 59-16323 propose to use base metals for the inner electrode of a monolithic capacitor.